The invention relates to a system and method for supplying voltage to electrical loads in the onboard electrical system of a motor vehicle.
In the case of known systems, the generator required for generating the voltage consumes a considerable amount of power, which has to be made available by the engine of the motor vehicle.
It is an object of the present invention to reduce the power to be provided by the motor vehicle engine for supplying the onboard electrical system of the motor vehicle with sufficient electric energy.
This object is achieved by a system and method for supplying the voltage to electrical loads in the onboard electrical system of a motor vehicle. The onboard electrical system includes at least two onboard electrical system regions. The first onboard electrical system region has an electric generator, a vehicle battery, as well as one or more first electrical loads. The second onboard electrical system region has a double-layer capacitor or a so-called supercap and one or more second electrical loads. Between the two onboard electrical system regions, a blocking device is provided, particularly a semiconductor diode or a power switch, which permits a current flow from the first onboard electrical system region into the second electrical system region and largely prevents a reverse current flow from the second onboard electrical system region into the first onboard electrical system region. The output voltage of the electric generator is raised and the supercap is charged when there is a falling below a first threshold value of the electric voltage in the second onboard electrical system region. Advantageous embodiments of the invention are described herein.
According to the invention, the electrical loads in the onboard electrical system of a motor vehicle are divided into a group of at least two types of electrical loads. The first group of electrical (non-sensitive) loads will also operate reliably when there are relatively wide voltage fluctuations and/or when the voltage is relatively low; for example, when, in the case of a 12 volt onboard electrical system, the voltage falls below 10 volts and/or fluctuates between approximately 9 and 16 volts.
In contrast, the second group of electrical (sensitive) loads will operate reliably only when there are relatively slight voltage fluctuations about the nominal voltage; for example, when, in the case of a 12 volt onboard electrical system, the voltage fluctuates only between approximately 11 and 13 volts. According to the invention, the onboard electrical system is divided into at least two electrical system regions; the non-sensitive electrical loads are arranged in the first electrical system region, and the sensitive electrical loads are arranged in the second electrical system region.
A current flow from the second onboard electrical system region into the first onboard electrical system region, according to the invention, is largely prevented by a blocking device or circuit, preferably a semiconductor diode arranged between the first and the second electrical system region. In the first onboard electrical system region, the electric generator and a vehicle battery are arranged in parallel to the first electrical loads, and in the second onboard electrical system region, an energy accumulator, a battery or a capacitor, preferably a double-layer capacitor or a so-called supercap, is arranged in parallel to the second electrical loads. During operation of the motor vehicle, the double-layer capacitor is regularly charged to a voltage which keeps the sensitive second electrical loads ready to operate while it discharges.
During the phases in which the double-layer capacitor does not have to be charged, the voltage of the generator is reduced to such an extent that the operational readiness of the first electrical loads (still) exists (see DE 2006 002 985). In this case, the voltage at the double-layer capacitor is higher than at the first (non-sensitive) loads, and the blocking device or diode prevents the discharge of the double-layer capacitor by way of the loads of the first onboard electrical system region. Inversely, the blocking device permits an electric current flow from the electric generator by way of the blocking device or diode into the second onboard electrical system region when the output voltage of the generator is raised in order to charge the double-layer capacitor.
The monitoring of the charge condition or of the output voltage of the double-layer capacitor takes place by way of a charge control device or a control/power unit which controls the generator such that, when the capacitor voltage falls below a threshold voltage, the generator increases the voltage for charging and subsequently reduces it again.
In contrast to the known state of the art, the generator can be controlled such that, during operation of the motor vehicle, it predominantly provides only a lower voltage for operating the non-sensitive loads. In the case of the known state of the art, it was, however, necessary to lastingly raise the voltage to such an extent that even the sensitive loads always had a sufficient operating voltage available.
Thus, by means of the solution according to the invention, the power consumption of the generator can be reduced for long periods of time and the fuel consumption and the CO2 emission of the motor vehicle can thereby clearly be reduced.
In a particularly advantageous embodiment of the invention, it is provided that precharging and/or coupling or separating of the supercap to the onboard electrical system or from the onboard electrical system takes place by a separate control/power unit. The control/power unit preferably also carries out the diagnosis of the supercap, particularly a capacitance and/or resistance determination, during the precharging operation. As a result of this measure, the supercap can be smoothly integrated into the onboard electrical system of a vehicle.
In a further development of the invention, it is provided that, during precharging or charging of the supercap to the onboard electrical system voltage of the second electrical system region, the temperature of the supercap is measured and is compared with a maximal value. As an alternative or in addition, a fault memory assigned to the supercap is read out, preferably in the control/power unit.
According to the invention, the fault memory preferably has a fault input if, in the past, a comparison of the capacitance (C) values present at the time and/or of the resistance (R) values of the supercap with stored temperature-dependent or charging-current-dependent characteristic values of the supercap pointed to the presence of a fault at the supercap. On the basis of these diagnoses, disturbances of the onboard electrical system as a result of a faulty supercap can be avoided.
In the case of a preferred further development of the system according to the invention, it is provided that, when the supercap falls below a maximal temperature value and the fault input is absent, the supercap is charged to the actual voltage of the second onboard electrical system region or to largely the actual voltage of the second onboard electrical system region, before the supercap is electrically connected with the second onboard electrical system region. The supercap subsequently stabilizes the voltage in the second onboard electrical system region. This measures allows a careful coupling of the supercap to the electrical system of the vehicle.
As a further development of the invention, it is provided that, when the terminal R and/or the terminal 15 are currentless and/or the doors are locked for longer than a predetermined time period, the supercap is discharged to approximately 9 volts by way of a feed back into the onboard electrical system, and is then electrically uncoupled from the onboard electrical system. As a result, a careful uncoupling of the supercap from the onboard electrical system is achieved, and the electrical system is relieved because of the otherwise high quiescent current requirement of the supercap.
In addition, by way of the above-mentioned measures, the charging operation is optimized, particularly with respect to a further reduction of the CO2 emission.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.